QUICKIE/FUNFACT: The Torah describes the three kinds of Tzaraas as SEIS, SAPACHAS, AND BAHERES. (13:2) How do these words relate to this spiritual disease?
There is a novelty in Halacha that is recognized in this week's Parsha when discussing the topic of the Metzorah (loosely translated as a leper, I believe that it has been proven that this is not the proper translation anymore). The Torah states that after a Metzorah has been afflicted with Tzaraas on every inch of his/her body, instead of being considered tainted, they are considered to be entirely pure! This seems to be nothing short of a phenomenon that only makes sense within the context of Judaism. How can something so tainted really be pure?!
While discussing this topic Rav Shimon Schwab Zt"l says in his Sefer Me'in Beis HaShoeva, that Tumah does not have a life of its own, it 'survives' off of purity. If there is no purity to feed off of the impurity can no longer live. In this manner the person whose body has been totally taken over by the tzaraas is considered to be pure. Throughout the time that his/her affliction was growing it could only survive because of its ability to continue in growth. At the point when it has used up all of its potential and it can no longer grow, the person is pure.
It is also said, in the (Gemara Sanhedrin 97a) "R' Yitzchak says, 'The Messiah will come only when the entire kingdom has switched to heretics'. We can properly explain the Gemara in Sanhedrin that speaks about the kingdom full of heretics bringing the Messiah. If the town has any signs of good, there is still room for negative influence, thus stunting the growth of anything positive. On the opposite side of the coin, if the town is full of heretics there is no more room for evil to grow thus sparking the beginning of the Geula.
This same idea was realized during the time of the Meraglim. (Bamidbar 13:27) Before the spies said anything negative about the land of Israel they introduced their observations with an inkling of truth about the land. With this they were believed by the people. Without this inkling of truth they had no credibility.
It sometimes seems that we have reached the bottom of the barrel and that we can no longer go any deeper in sin. We feel that we are forever abandoned by our creator. It is at this point however, when we are most susceptible to do Teshuva and to be the purest that we have ever been.*
*Imrei Baruch by R' Baruch Simon Shlit"a